The primary purpose of the enlarged supply of clean inbred rodents from the rodent production center contracts is to: maintain the approximately 100,000 breeding animals for hybrid proguction, e.g., B6D2F1, B6C3F1, which are used for cancer research throughout the DCT program; and supply cancer research laboratories with the large number of clean inbred animals needed for tumor transplantation. Obviously, it would be impossible to maintain the continuity of the experimental DCT cancer research program without the contribution of the Rodent Production Center Contracts.